Electrochemical reaction cell stack

Abstract

To suppress the occurrence of cracks on a joint surface between a glass seal part and a metal member and the peeling of the glass seal part from the metal member.SOLUTION: A stack that causes an electrochemical reaction includes a single cell including a fuel electrode, an electrolyte layer, and an air electrode, a metal member made of a chromium-containing alloy and having an oxide film on a surface thereof, and a glass seal member that is interposed between the metal member and another member or between the metal member and the single cell and is in contact with the oxide film, wherein the oxide film contains at least one of the following components i) and ii): i) at least one of: a) TiO and Ti2O3; b) TiO2ii; at least one of: c) NbO and Nb2O3; and d) at least one of: NbO2 and Nb2O5 SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The technology disclosed herein relates to an electrochemical reaction cell stack. [Background technology]

[0002] Solid oxide fuel cells (SOFCs) are known as one type of fuel cell that generates electricity using the electrochemical reaction between hydrogen and oxygen. SOFCs are generally used in the form of fuel cell stacks. Conventionally, a cell stack is known that comprises a plurality of fuel cell cells, an alloy member made of an alloy material containing chromium (Cr), and a glass seal that joins the alloy member and the fuel cell cells (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-107593 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] A chromium-containing oxide film exists on the surface of alloy components containing chromium. The glass seal is in contact with this oxide film. During the operation of the cell stack, a high voltage may be applied to the glass seal, which can extract oxygen ions from the oxide film, causing the oxide film to be reduced. In addition, since the fuel gas supplied to the cell stack is a hydrogen-rich reducing gas, the atmosphere around the alloy components may become reducing, which can also reduce the oxide film. In such cases, there is a concern that cracks may occur in the oxide film or at the joint between the oxide film and the glass seal, or that the glass seal may peel off from the oxide film. This problem is particularly pronounced in pure hydrogen power generation, where hydrogen gas is used as the fuel gas, as the atmosphere around the alloy components becomes strongly reducing.

[0005] These challenges are also common to electrolytic cell stacks, which consist of multiple electrolytic cell units, the constituent units of solid oxide type electrolytic cells (hereinafter referred to as "SOECs") that produce hydrogen using the electrolysis reaction of water. Furthermore, these challenges are not limited to SOFCs and SOECs, but are common to other types of electrochemical reaction cell stacks as well.

[0006] This specification discloses a technology capable of solving the above-mentioned problems. [Means for solving the problem]

[0007] The technologies disclosed herein can be implemented, for example, in the following forms: (1) The electrochemical reaction cell stack disclosed herein comprises a single cell including a fuel electrode, an electrolyte layer, and an air electrode; a metal member made of a chromium-containing alloy having an oxide film on its surface; and a glass seal portion interposed between the metal member and other members, or between the metal member and the single cell, and in contact with the oxide film, wherein the oxide film contains at least one of the following components i) and ii). i) a) and b) below a) At least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below c) At least one of NbO and Nb2O3 d) At least one of NbO2 and Nb2O5

[0008] According to the above configuration, the occurrence of cracks at the joint surface between the glass seal and the metal member, and the peeling of the glass seal from the metal member are suppressed.

[0009] (2) In the electrochemical reaction cell stack described in (1) above, the oxide film has a contact region that is in contact with the glass seal portion and a non-contact region that is not in contact with the glass seal portion, and at least one of the components i) and ii) may be included in a proximity region of the non-contact region where the distance measured along the surface of the oxide film from the boundary position with the contact region is 100 μm or less.

[0010] With this configuration, the occurrence of cracks at the joint surface between the glass seal and the metal member, and the peeling of the glass seal from the metal member are effectively suppressed.

[0011] (3) In the electrochemical reaction cell stack described in (2) above, the content of components i) and ii) in the adjacent region, calculated as TiO2 and NbO2, may be 0.1% by mass or more and 10% by mass or less.

[0012] With this configuration, the occurrence of cracks at the joint surface between the glass seal and the metal member, and the peeling of the glass seal from the metal member are effectively suppressed.

[0013] (4) In the electrochemical reaction cell stack described in any one of (1) to (3) above, the glass seal portion may be made of SiO2-B2O3-MgO glass.

[0014] The thermal expansion coefficient of SiO2-B2O3-MgO glass is close to that of chromium-containing alloys. If the glass seal is made of SiO2-B2O3-MgO glass, the occurrence of cracks at the joint between the glass seal and the metal component, and the delamination of the glass seal from the metal component are effectively suppressed.

[0015] (5) Other electrochemical reaction cell stacks disclosed by this specification include a single cell including a fuel electrode, an electrolyte layer, and an air electrode, a metal member made of a chromium-containing alloy having an oxide film on its surface, and a glass seal portion interposed between the metal member and another member or between the metal member and the single cell and contacting the oxide film. The oxide film contains the following components e) and f). e) At least one of MO and M2O3 f) At least one of MO2 and M2O5 (However, M is a transition metal element excluding chromium)

[0016] According to the above configuration, the generation of cracks at the joint surface between the glass seal portion and the metal member and the peeling of the glass seal portion from the metal member are suppressed.

Brief Description of the Drawings

[0017] [Figure 1] Perspective view showing the external configuration of the fuel cell stack of the first embodiment [Figure 2] Cross-sectional view showing the fuel cell stack of the first embodiment cut along line II-II of FIG. 1 [Figure 3] Cross-sectional view showing the fuel cell stack of the first embodiment cut along line III-III of FIG. 1 [Figure 4] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment cut at the same position as line II-II of FIG. 1 [Figure 5] Cross-sectional view showing two adjacent electrochemical reaction units in the fuel cell stack of the first embodiment cut at the same position as line III-III of FIG. 1 [Figure 6] Enlarged view within the frame F of FIG. 5 [Figure 7] Partial enlarged cross-sectional view showing an enlarged view of the periphery of the glass seal portion in the fuel cell stack of the modified example

Modes for Carrying Out the Invention

[0018] <00001​​A-1. Configuration of fuel cell stack 10: The first embodiment will be described with reference to Figures 1 to 6. The fuel cell stack 10 of this embodiment (an example of an electrochemical reaction cell stack) is used in a solid oxide type fuel cell that includes an electrolyte layer 112 containing solid oxides.

[0019] (Overall configuration of fuel cell stack 10) As shown in Figures 1 to 3, the fuel cell stack 10 comprises a power generation block 100, an end separator 230, a first plate 232, a second plate 260, a first terminal plate 240, a second terminal plate 250, an insulating section 220, a first end plate 210, a second end plate 270, four gas passage members 280, and a glass seal section 135. The first end plate 210, the insulating section 220, the end separator 230, the first terminal plate 240, the power generation block 100, the second terminal plate 250, the second plate 260, and the second end plate 270 have roughly the same rectangular shape and are arranged in this order overlapping in a predetermined arrangement direction (up and down direction in Figure 2).

[0020] As shown in Figures 2 and 3, the power generation block 100 is composed of a plurality (seven in this embodiment) of electrochemical reaction units 100U (hereinafter sometimes abbreviated as "reaction unit 100U") arranged in a predetermined arrangement direction (up and down direction in Figure 2).

[0021] As shown in Figure 1, the fuel cell stack 10 has bolt holes BH near each of its four corners, each extending from the first end plate 210 to the second end plate 270. A bolt B is inserted into each bolt hole BH. Nuts N are threaded onto both ends of each bolt B. These bolts B and nuts N fasten the components from the first end plate 210 to the second end plate 270 together. As shown in Figures 2 and 3, the first plate 232 is supported by the end separator 230, and the four gas passage members 280 are connected to the second end plate 270.

[0022] (Overall composition of an electrochemical reaction unit of 100U) As shown in Figures 4 and 5, the electrochemical reaction unit 100U comprises a single cell 110, a single cell separator 120 (an example of a metal component), an air electrode frame 130, a glass seal portion 135, a fuel electrode frame 140, a fuel electrode current collector 144, two interconnectors 190, and two IC separators 180. One IC separator 180 (an example of another component), the air electrode frame 130, the single cell separator 120, the fuel electrode frame 140, and the other IC separator 180 are arranged in this order. The single cell 110 is supported by the single cell separator 120, the two interconnectors 190 are each supported by the two IC separators 180, and the fuel electrode current collector 144 is positioned between the single cell 110 and the interconnectors 190.

[0023] As shown in Figures 4 and 5, the IC separator 180 and interconnector 190 are shared by two adjacent reaction units 100U. However, as shown in Figure 2, one of the multiple reaction units 100U located at one end (the lower end in Figure 2) does not have an IC separator 180 and interconnector 190 adjacent to the fuel electrode frame 140, and the second terminal plate 250 is superimposed on the fuel electrode frame 140.

[0024] (Single cell 110) The single cell 110 comprises an electrolyte layer 112, an air electrode 114, and a fuel electrode 116. As shown in Figures 4 and 5, the air electrode 114, the electrolyte layer 112, and the fuel electrode 116 are arranged in this order, with a reaction prevention layer 118 interposed between the electrolyte layer 112 and the air electrode 114. The single cell 110 of this embodiment is a fuel electrode-supported single cell in which the other layers constituting the single cell 110 (electrolyte layer 112, air electrode 114, and reaction prevention layer 118) are supported by the fuel electrode 116.

[0025] The electrolyte layer 112 is a rectangular, flat member having one side on which the air electrode 114 is located (the upper side in Figures 4 and 5) and another side parallel to the air electrode 116 (the lower side in Figures 4 and 5). The electrolyte layer 112 is a layer containing a solid oxide (for example, YSZ (yttria-stabilized zirconia)). The air electrode 114 is a layer having a rectangular shape smaller than the electrolyte layer 112 and contains, for example, a perovskite-type oxide (for example, LSCF (lanthanum strontium cobalt iron oxide)). The fuel electrode 116 is a layer having a rectangular shape approximately the same size as the electrolyte layer 112 and contains, for example, Ni (nickel), a cermet made of Ni and ceramic particles, a Ni-based alloy, etc. The reaction prevention layer 118 is a layer having a rectangular shape approximately the same size as the air electrode 114 and contains, for example, GDC (gadolinium-doped ceria). The reaction prevention layer 118 has the function of suppressing the reaction of elements (e.g., Sr) diffused from the air electrode 114 with elements (e.g., Zr) contained in the electrolyte layer 112 to produce a highly resistive substance (e.g., SrZrO3).

[0026] (Single-cell separator 120) As shown in Figures 4 and 5, the single-cell separator 120 is a rectangular frame-shaped member having a roughly rectangular through-hole 121 near the center, and is made of, for example, metal. The thickness of the single-cell separator 120 is relatively thin, for example, 0.05 mm or more and 0.2 mm or less. The periphery of the through-hole 121 in the single-cell separator 120 is joined to the periphery of one surface of the electrolyte layer 112 (the surface on which the air electrode 114 is located: the upper surface in Figures 4 and 5) by a sealing material 124. The sealing material 124 is made of, for example, brazing material (Ag brazing).

[0027] (Air pole frame 130) As shown in Figures 4 and 5, the air electrode frame 130 is a rectangular frame-shaped member having a substantially rectangular through hole 131 near the center, and is formed of, for example, an insulating ceramic (such as mica). The thickness of the air electrode frame 130 is preferably 0.5-5 mm. The air electrode frame 130 has two sealing holes 132 located on both sides of the through hole 131.

[0028] (Glass seal portion 135) Each air electrode frame 130 has two sealing holes 132, each containing one glass seal portion 135. The glass seal portion 135 is a cylindrical member with openings at both ends and is made of crystallized glass. One end of the glass seal portion 135 is joined to the single-cell separator 120, and the other end is joined to the IC separator 180.

[0029] (Fuel pole frame 140) As shown in Figure 5, the fuel electrode frame 140 is a rectangular frame-shaped member having a roughly rectangular through-hole 141 near the center, and is formed of, for example, metal.

[0030] (IC separator 180) As shown in Figures 4 and 5, the IC separator 180 is a rectangular frame-shaped member having a through hole 181 near the center, and is made of a metal such as ferritic stainless steel.

[0031] (Interconnector 190, and fuel electrode current collector 144) As shown in Figures 4 and 5, the interconnector 190 comprises a rectangular flat plate portion 191, a plurality of plate-shaped air electrode current collectors 192 protruding from one surface of the flat plate portion 191 toward the air electrode 114, and a coating layer 193. The flat plate portion 191 and the air electrode current collectors 192 are conductive and made of metal (for example, ferritic stainless steel). The coating layer 193 is conductive and is arranged to cover the surface of the air electrode current collectors 192 and the surface of the flat plate portion 191 on which the air electrode current collectors 192 are arranged. The flat plate portion 191 is joined to the periphery of the through hole 181 in the IC separator 180, for example, by welding.

[0032] The fuel electrode current collector 144 is a member that connects the interconnector 190 and the fuel electrode 116, and is formed of a conductive material such as nickel, a nickel alloy, or stainless steel. As shown in Figures 4 and 5, the fuel electrode current collector 144 comprises an interconnector-facing portion 146, an electrode-facing portion 145 parallel to the interconnector-facing portion 146, and a connecting portion 147 connecting the electrode-facing portion 145 and the interconnector-facing portion 146, and is U-shaped overall. The electrode-facing portion 145 is in contact with the fuel electrode 116, and the interconnector-facing portion 146 is in contact with the flat plate portion 191 of the interconnector 190.

[0033] As described above, the interconnector 190 is shared by two adjacent reaction units 100U. More specifically, as shown in Figures 4 and 5, the air electrode current collector 192 is joined to the air electrode 114 of a single cell 110 provided in one of the two adjacent reaction units 100U via a conductive bonding material 196 made of, for example, a spinel-type oxide, thereby electrically connecting to the air electrode 114. The flat plate portion 191 is electrically connected to the fuel electrode 116 of a single cell 110 provided in the other of the two adjacent reaction units 100U via a fuel electrode current collector 144. This ensures electrical conductivity between the two adjacent reaction units 100U.

[0034] However, as described above, the reaction unit 100U located at one end (the lower end of Figure 2) of the multiple reaction units 100U does not have an interconnector 190 on the fuel electrode 116 side. The fuel electrode 116 provided in this reaction unit 100U is connected to the second terminal plate 250 via a fuel electrode current collector 144.

[0035] A spacer 149, for example made of mica, is placed between the electrode facing portion 145 and the interconnect facing portion 146. As a result, the fuel electrode current collector 144 follows the deformation of the reaction unit 100U due to temperature cycles and reaction gas pressure fluctuations, and the electrical connection between the fuel electrode 116 and the interconnect 190 (or second terminal plate 250) via the fuel electrode current collector 144 is maintained well.

[0036] (Air chamber 313 and fuel chamber 323) As shown in Figures 4 and 5, the space partitioned by the single-cell separator 120 and single cell 110, the air electrode frame 130, the IC separator 180 and interconnector 190 faces the air electrode 114 and forms an air chamber 313 through which the oxidizer gas OG flows. The air electrode frame 130 partitions the air chamber 313 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the air chamber 313 into the outside space.

[0037] Furthermore, the space partitioned by the single-cell separator 120 and single cell 110, the fuel electrode frame 140, the IC separator 180 and interconnector 190 faces the fuel electrode 116 and forms a fuel chamber 323 through which fuel gas FG flows. The fuel electrode frame 140 partitions the fuel chamber 323 from the outside space around its entire circumference and seals the space between the single-cell separator 120 and the IC separator 180, preventing gas from leaking from the fuel chamber 323 into the outside space.

[0038] The single-cell separator 120 separates the air chamber 313 from the fuel chamber 323, suppressing gas leakage (cross-leakage) from the air electrode 114 to the fuel electrode 116, or from the fuel electrode 116 to the air electrode 114, around the single-cell 110. In addition, the IC separator 180 and interconnector 190 suppress gas leakage between adjacent reaction units 100U.

[0039] (First end plate 210) The first end plate 210 is a member formed by press-forming (bending) a single plate-shaped member. The first end plate 210 is made of a metal such as stainless steel. As shown in Figures 1-3, the first end plate 210 comprises a rectangular frame-shaped planar portion 211 having a through hole 212 near the center, and an outer projection 213 and an inner projection 214 that project from the planar portion 211 in the opposite direction to the insulating portion 220 (upwards in Figure 2). The planar portion 211 has holes that constitute the bolt holes BH described above. The outer projection 213 protrudes from the outer peripheral edge of the planar portion 211. The outer projection 213 is formed around the entire circumference of the outer peripheral portion of the planar portion 211. The inner projection 214 protrudes from the inner peripheral edge of the planar portion 211. The inner projection 214 is formed around the entire circumference of the inner peripheral portion of the planar portion 211.

[0040] (Insulation part 220) The insulating portion 220 is a rectangular frame-shaped member having a through hole near the center, and is formed of an insulating material such as crystallized glass, mica, forsterite, or other insulating ceramics. As shown in Figure 2, the insulating portion 220 is sandwiched between the first end plate 210 and the end separator 230, thereby ensuring insulation between the first end plate 210 and the end separator 230.

[0041] (End separator 230) As shown in Figures 2 and 3, the end separator 230 is a rectangular frame-shaped member having a through hole 231 near the center, and is made of, for example, metal.

[0042] (Plate 1, No. 232) The first plate 232 is a rectangular, flat member made of a conductive material such as stainless steel. As shown in Figures 2 and 3, the first plate 232 is joined to the peripheral portion of the through hole 231 in the end separator 230, for example, by welding. The end separator 230 and the first plate 232 separate the power generation block 100 from the external space of the fuel cell stack 10.

[0043] The first plate 232 is connected to an interconnector 190, described later, provided on a reaction unit 100U located at one end (the upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via a connecting member having the same structure as the fuel electrode current collector 144, described later. This electrically connects the reaction unit 100U and the first plate 232.

[0044] (Terminal 1 Plate 240) The first terminal plate 240 is a rectangular frame-shaped member having a through hole 241 near the center, and is made of a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The first terminal plate 240 is electrically connected to a reaction unit 100U located at one end (upper end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100, via the first plate 232 and the end separator 230. One end of the first terminal plate 240 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the positive output terminal of the fuel cell stack 10.

[0045] (Terminal 2 Plate 250) The second terminal plate 250 is a rectangular plate-shaped member, formed from a conductive material such as ferritic stainless steel that forms an alumina oxide film on its surface. The second terminal plate 250 is electrically connected to the reaction unit 100U located at the other end (lower end in Figure 2) of the multiple reaction units 100U that constitute the power generation block 100. One end of the second terminal plate 250 (right end in Figure 2) protrudes laterally from the power generation block 100, and this protruding portion functions as the negative output terminal of the fuel cell stack 10.

[0046] (Plate 2, page 260) The second plate 260 is a rectangular, flat member, formed of, for example, an insulating material. The peripheral edge of the second plate 260 is sandwiched between the second terminal plate 250 and the second end plate 270, thereby ensuring insulation between the second terminal plate 250 and the second end plate 270.

[0047] (Second end plate 270) The second end plate 270 is a member formed by press-forming (bending) a single plate-shaped member, and is made of a conductive material such as stainless steel. The second end plate 270 comprises a rectangular frame-shaped planar portion 271 having a through hole 272 near the center, and an outer projection 273 and an inner projection 274 projecting from the planar portion 271 in the opposite direction to the second terminal plate 250 (downward in Figure 2). The planar portion 271 has holes that constitute the bolt holes BH described above. The outer projection 273 protrudes from the outer peripheral edge of the planar portion 271. The outer projection 273 is formed around the entire circumference of the outer peripheral portion of the planar portion 271. The inner projection 274 protrudes from the inner peripheral edge of the planar portion 271. The inner projection 274 is formed around the entire circumference of the inner peripheral portion of the planar portion 271.

[0048] (Manifolds 311, 312, 321, 322) As shown in Figures 1, 2, and 3, the fuel cell stack 10 has four holes that penetrate from the power generation block 100 to the second end plate 270. The four holes are the oxidizer gas supply manifold 311, the oxidizer gas discharge manifold 312, the fuel gas supply manifold 321, and the fuel gas discharge manifold 322, respectively.

[0049] As shown in Figure 2, the oxidizer gas supply manifold 311 is a gas flow path that supplies oxidizer gas OG, introduced from outside the fuel cell stack 10, to the air chambers 313 (described later) of each reaction unit 100U. The oxidizer gas discharge manifold 312 is a gas flow path that discharges oxidizer off-gas OOG, discharged from the air chambers 313 of each reaction unit 100U, to the outside of the fuel cell stack 10. For example, air is used as the oxidizer gas OG.

[0050] As shown in Figure 3, the fuel gas supply manifold 321 is a gas flow path that supplies fuel gas FG introduced from outside the fuel cell stack 10 to the fuel chamber 323 (described later) of each reaction unit 100U. The fuel gas discharge manifold 322 is a gas flow path that discharges fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the outside of the fuel cell stack 10. As the fuel gas FG, for example, hydrogen-rich gas obtained by reforming city gas is used.

[0051] As shown in Figure 5, the fuel gas supply manifold 321 penetrates one of the two glass seal portions 135 located inside each air electrode frame 130. In other words, the internal space of the glass seal portion 135 constitutes part of the fuel gas supply manifold 321. Similarly, the fuel gas discharge manifold 322 penetrates the other of the two glass seal portions 135 located inside each air electrode frame 130. In other words, the internal space of the glass seal portion 135 constitutes part of the fuel gas discharge manifold 322. The glass seal portions 135 suppress leakage of fuel gas FG or fuel off-gas FOG from the fuel gas supply manifold 321 and the fuel gas discharge manifold 322 through the interface between the air electrode frame 130 and the single-cell separator 120, and the interface between the air electrode frame 130 and the IC separator 180.

[0052] (Gas passage member 280) Each of the four gas passage members 280 comprises a main body portion 281 and a flange portion 282, as shown in Figures 1 to 3. The main body portion 281 has a gas through-hole 283 that penetrates vertically. The flange portion 282 is provided so as to protrude outward from the other end of the main body portion 281 (the lower end in Figure 2). The flange portion 282 has a plurality of bolt holes 284. Bolts (not shown) for connecting the fuel cell stack 10 to an external device are inserted into each bolt hole 284. One end of the main body portion 281 provided on the four gas passage members 280 (the upper end in Figures 2 and 3) is joined to the second end plate 270, for example by welding, and the gas through-holes 283 communicate with manifolds 311, 312, 321, and 322, respectively. Gas piping (not shown) for gas supply or discharge is connected to each main body portion 281.

[0053] A-2. Operation of the fuel cell stack 10: As shown in Figure 2, the oxidizer gas OG is supplied to the air chamber 313 through the gas passage member 280 and the oxidizer gas supply manifold 311. Also, as shown in Figure 3, the fuel gas FG is supplied to the fuel chamber 323 through the gas passage member 280 and the fuel gas supply manifold 321.

[0054] When oxidant gas OG is supplied to the air chamber 313 of each reaction unit 100U and fuel gas FG is supplied to the fuel chamber 323, electricity is generated in the single cell 110 by an electrochemical reaction between the oxidant gas OG and fuel gas FG. This power generation reaction is an exothermic reaction. As described above, the interconnector 190 is shared by two adjacent reaction units 100U, and the interconnector 190 ensures conductivity between the two adjacent reaction units 100U. In other words, the multiple reaction units 100U included in the fuel cell stack 10 are electrically connected in series. Furthermore, the second terminal plate 250 is electrically connected to the reaction unit 100U located at one end (the lower end of Figure 2), and the first terminal plate 240 is electrically connected to the reaction unit 100U located at the other end (the upper end of Figure 2). As a result, the electrical energy generated in each reaction unit 100U is extracted from the terminal plates 240 and 250, which function as output terminals of the fuel cell stack 10. Since SOFCs generate electricity at relatively high temperatures (for example, 700°C to 1000°C), the fuel cell stack 10 may be heated by a heater (not shown) after startup until the high temperature can be maintained by the heat generated by power generation.

[0055] As shown in Figure 2, the oxidizer off-gas OOG discharged from the air chamber 313 of each reaction unit 100U to the oxidizer gas discharge manifold 312 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281. Also, as shown in Figure 3, the fuel off-gas FOG discharged from the fuel chamber 323 of each reaction unit 100U to the fuel gas discharge manifold 322 is discharged to the outside of the fuel cell stack 10 through the internal space of the main body 281.

[0056] A-3. Detailed composition of oxide film 122: In this embodiment, the single-cell separator 120 is a ferritic stainless steel containing Ti (titanium), Al (aluminum), and Cr, and has an oxide film 122 on its surface mainly composed of alumina (Al2O3) containing Cr.

[0057] As shown in Figure 6, one end of the glass seal portion 135 is in contact with the single-cell separator 120. The glass seal portion 135 is made of SiO2-B2O3-MgO glass and has a thermal expansion coefficient close to that of the single-cell separator 120, which is made of a chromium-containing alloy.

[0058] Of the oxide film 122, the region in contact with the glass seal portion 135 is the contact region Ar1, and the region that does not come into contact with the glass seal portion 135 is the non-contact region Ar2. Of the non-contact region Ar2, the region where the distance L measured along the surface of the oxide film 122 from the boundary position with the contact region Ar1 is 100 μm or less is the adjacent region Ar2n.

[0059] The oxide film 122 may contain at least one of the following components i) and ii). i) a) and b) below a) At least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below c) At least one of NbO and Nb2O3 d) At least one of NbO2 and Nb2O5

[0060] During operation of the fuel cell stack 10, a high voltage may be applied to the glass seal portion 135, causing oxygen ions to be extracted from the oxide film 122 and reducing the oxide film. When the oxide film 122 is reduced, the decrease in oxygen ions within the oxide film 122 disrupts the charge balance, increasing the repulsion due to Coulomb force, and causing the oxide film 122 to expand. This phenomenon is not limited to the oxide film 122, which is mainly composed of alumina, but is a phenomenon common to oxides.

[0061] If the oxide film 122 contains component i), i.e., titanium oxide, then component a) plays a role in suppressing the reduction of the oxide film 122. Since titanium oxide is less easily reduced than oxides containing chromium, an increase in the amount of titanium oxide dissolved in the oxide film 122 suppresses the reduction of the oxide film 122 as a whole. Generally, the ease of solid solution depends on the valency of the metal element contained in the substance being dissolved, and substances containing elements with the same valency as the metal element contained in the substance constituting the oxide film 122 (the substance being dissolved) are more easily dissolved. Since the valencies of the metal elements contained in the substance constituting a typical oxide film 122 are divalent or trivalent, divalent TiO and trivalent Ti2O3 are more easily dissolved than tetravalent TiO2. The presence of component a), which is relatively easily dissolved, in the oxide film 122 suppresses the reduction of the oxide film 122.

[0062] On the other hand, component b) improves the bonding strength of the single-cell separator 120 to the glass seal portion 135 and contributes to suppressing peeling of the single-cell separator 120 from the glass seal portion 135. The reason why component b) contributes to the improvement of bonding strength is not entirely clear, but it is speculated as follows: Since the glass and the oxide film are bonded by ionic bonds, it is thought that substances containing elements with a similar valency to Si, which is contained in SiO2 that determines the structure of the glass, bond more easily with the glass. Since the valency of Si contained in SiO2 is tetravalent, tetravalent TiO2 is thought to bond more easily with the glass than divalent TiO or trivalent Ti2O3, thus contributing to the improvement of bonding strength.

[0063] Therefore, when titanium oxide is solid-dissolved in the oxide film 122, the presence of both component a) and component b) in the oxide film 122 effectively suppresses the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, as well as the delamination of the glass seal portion 135 from the single-cell separator 120. In particular, it is effective that both component a) and component b) are present in the adjacent Ar2n region, which is prone to becoming the starting point for cracks and delamination.

[0064] The same applies when component ii), i.e., niobium oxide, is solid-dissolved in the oxide film 122. In other words, by including both component c), which is relatively easily solid-dissolved, and component d), which contributes to improving bonding strength, the occurrence of cracks at the bonding surface between the glass seal portion 135 and the single-cell separator 120, and the delamination of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed. In particular, it is effective when both component c) and component d) are included in the adjacent region Ar2n.

[0065] The same applies when oxides of transition metal elements other than titanium oxide and niobium oxide are solid-dissolved in the oxide film 122. In other words, the oxide film 122 may contain both component e) and component f) below. By containing both component e), which is relatively easily solid-dissolved, and component f), which contributes to improving bonding strength, the occurrence of cracks at the bonding surface between the glass seal portion 135 and the single-cell separator 120, and the peeling of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed. e) At least one of MO and M2O3 f) At least one of MO2 and M2O5 (However, M represents transition metal elements excluding chromium.)

[0066] The content of components i) and ii) in the adjacent region Ar2n may be between 0.1% by mass and 10% by mass. If the content is within this range, a sufficient crack and delamination suppression effect can be obtained. In this specification, "the content of components i) and ii) in the adjacent region" is the ratio of the mass of components i) and ii) to the total mass of the inclusions contained in the adjacent region. Furthermore, if only one of components i) or ii) is contained in the adjacent region Ar2n, it is the content of that component; if both are contained, it is the sum of the content of components i) and ii). The content of component i) is the content in terms of TiO2, that is, the content calculated assuming that all the Ti contained in the adjacent region Ar2n exists as TiO2. Similarly, the content of component ii) is the content in terms of NbO2, that is, the content calculated assuming that all the Nb contained in the adjacent region Ar2n exists as NbO2.

[0067] A-4. Manufacturing method of fuel cell stack 10: An example of a manufacturing method for the fuel cell stack 10 with the above configuration is described below.

[0068] When the oxide film 122 contains components a) and b), a plate material made of an alloy containing Ti and Cr is prepared as the material for the single-cell separator 120. This plate material is heat-treated, for example, at 1000°C in an atmospheric environment to form an oxide film 122 on its surface. After the oxide film 122 is formed, the plate material is subjected to the necessary processing to obtain the single-cell separator 120.

[0069] The single-cell separator 120 is stacked with other components to assemble the fuel cell stack 10. The assembled fuel cell stack 10 is heat-treated at a heat treatment temperature higher than the operating temperature to bond the glass seal portion 135 and the single-cell separator 120. The heat treatment temperature is, for example, 800°C or higher. The solid solution of titanium oxide into the oxide film 122 proceeds as the Ti contained in the alloy material of the single-cell separator 120 diffuses into the oxide film 122 during the heat treatment. The heat treatment is performed in a reducing atmosphere, that is, in an atmosphere where the partial pressure of oxygen is lower than that of air (for example, in the case of a heat treatment temperature of 850°C, 10 -25 ~10 -27 By performing the procedure at an atm (heat), or by holding the heat-treated fuel cell stack 10 in a reducing atmosphere for a certain period of time, the oxide film 122 can be made to contain both component a) and component b).

[0070] If the oxide film 122 contains components c) and d), the fuel cell stack 10 can be manufactured in the same procedure as above, except that a plate material made of an alloy containing Nb and Cr is prepared as the material for the single-cell separator 120. Similarly, if the oxide film 122 contains components e) and f), the fuel cell stack 10 can be manufactured in the same procedure as above, except that a plate material made of an alloy containing the desired transition metal M and Cr is prepared as the material for the single-cell separator 120.

[0071] A-5. Effects of this embodiment: As described above, the fuel cell stack 10 of this embodiment comprises a single cell 110 including a fuel electrode 116, an electrolyte layer 112, and an air electrode 114; a single cell separator 120 made of a chromium-containing alloy having an oxide film 122 on its surface; and a glass seal portion 135 interposed between the single cell separator 120 and the IC separator 180 and in contact with the oxide film 122, wherein the oxide film 122 contains at least one of the following components i) and ii). i) a) and b) below a) At least one of TiO and Ti2O3 b) TiO2 ii) c) and d) below c) At least one of NbO and Nb2O3 d) At least one of NbO2 and Nb2O5

[0072] According to the above configuration, the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, and the peeling of the glass seal portion 135 from the single-cell separator 120 are suppressed.

[0073] The oxide film 122 has a contact region Ar1 that is in contact with the glass seal portion 135 and a non-contact region Ar2 that is not in contact with the glass seal portion 135, and at least one of components i) and ii) is included in a nearby region Ar2n within the non-contact region Ar2, where the distance L measured along the surface of the oxide film 122 from the boundary position with the contact region Ar1 is 100 μm or less. With this configuration, the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, and the peeling of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed.

[0074] The content of components i) and ii) in the adjacent region of Ar2n, in terms of TiO2 and NbO2, is between 0.1% by mass and 10% by mass. With this configuration, the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, and the peeling of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed.

[0075] The glass seal portion 135 is made of SiO2-B2O3-MgO glass. Since the thermal expansion coefficient of SiO2-B2O3-MgO glass is close to that of chromium-containing alloys, the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, and the delamination of the glass seal portion 135 from the single-cell separator 120 are effectively suppressed.

[0076] Furthermore, even when the oxide film 122 contains components e) and f) below, the occurrence of cracks at the joint surface between the glass seal portion 135 and the single-cell separator 120, and the peeling of the glass seal portion 135 from the single-cell separator 120 are suppressed, similar to when the oxide film 122 contains component i) or component ii). e) At least one of MO and M2O3 f) At least one of MO2 and M2O5 (However, M represents transition metal elements excluding chromium.)

[0077] A-6. Performance evaluation: Samples of multiple metal components with different titanium oxide compositions in the oxide film were prepared, and voltage application tests were performed to check for the occurrence of cracks and delamination.

[0078] 1. Create a sample 1) Samples S1-S9 A ferritic stainless steel metal component containing Ti, Al, and Cr was heat-treated at 1000°C in an atmospheric environment to form an oxide film on its surface, mainly composed of alumina with solid-solution Cr. A glass seal made of SiO2-B2O3-MgO glass was sandwiched between the two metal components with the oxide film formed on them, and the glass seal and the metal components were joined by heat treatment at 850°C. The oxygen partial pressure during heat treatment was set to 10 -25 ~10 -27 By adjusting the temperature to atm, the composition of titanium oxide in the oxide film was adjusted to the state shown in Table 1, and samples S1-S9 were obtained.

[0079] 2) Samples S10-S18 A ferritic stainless steel metal component containing Ti and Cr was heat-treated at 1000°C in an atmospheric environment to form an oxide film mainly composed of chromium oxide (Cr2O3) on its surface. A glass seal made of SiO2-B2O3-MgO glass was sandwiched between the two metal components with the oxide film formed on them, and the glass seal and the metal components were joined by heat treatment at 850°C. The oxygen partial pressure during heat treatment was set to 10 -25 ~10 -27By adjusting to atm, the composition of titanium oxide in the oxide film was adjusted as shown in Table 1, and samples S10 - S18 were obtained.

[0080] 3) Measurement of the content ratio of titanium oxide Before subjecting Sample S1 to the voltage application test in 2. below, it was fractured within the oxide film so that the fracture surface included both the contact region and the proximity region in the oxide film and was parallel to the interface between the glass and the oxide film. The fracture surface was subjected to measurement by the XPS (X-ray Photoelectron Spectroscopy) method to determine the content ratio of titanium oxide in the oxide film. The measurement by the XPS method was performed with a beam diameter of 100 μm within the range where the binding energy was 452 eV or more and 468 eV or less. Ti2p derived from TiO 3 / 2 , Ti2p 1 / 2 peaks were at 455 eV and 461 eV respectively, and Ti2p derived from TiO2 3 / 2 , Ti2p 1 / 2 peaks were at 458 eV and 464 eV respectively. In principle, since the ratio of the Ti2p 3 / 2 peak area to the Ti2p 1 / 2 peak area is 2:1, the content ratio of TiO was fixed so that the ratio of the peak area of Ti2p 3 / 2 to the peak area of Ti2p 1 / 2 was 2:1 for fitting. The content ratio of TiO was determined using the total value of the peak areas of the fitted Ti2p 3 / 2 and Ti2p 1 / 2 . The content ratio of TiO2 was determined in the same manner. From the obtained TiO content ratio and TiO2 content ratio, the content ratio (molar ratio) of TiO and TiO2 in the oxide film was determined. Also, by performing SEM / EDX analysis on the same fracture surface as that subjected to the measurement by the XPS method, the content ratio (mass%) of titanium oxide in the oxide film was determined in terms of TiO2 conversion.

[0081] For Samples S2 - S18 as well, the content ratio of TiO and TiO2 in the oxide film and the content ratio of titanium oxide in the oxide film were determined by the same method.

[0082] 2. Voltage application test Samples S1-S18 obtained in 1. above were subjected to voltage application tests. The voltage application tests were performed by placing each sample in an electric furnace at 700°C and applying a voltage of 5V or 10V for 10 hours. The voltage was applied by connecting a cord connected to an external power supply to the metal member and other members. After the voltage application, each sample was allowed to cool to room temperature and subjected to a tensile test to observe the presence or absence of cracks and delamination at the joint surface between the oxide film of the metal member and the glass seal portion. Samples in which cracks or delamination were observed in the tensile test after applying a voltage of 5V were evaluated as ×, samples in which no cracks or delamination were observed in the tensile test after applying a voltage of 5V but cracks or delamination were observed in the tensile test after applying a voltage of 10V were evaluated as ○, and samples in which no cracks or delamination were observed in either the tensile test after applying a voltage of 5V or the tensile test after applying a voltage of 10V were evaluated as ◎.

[0083] [Table 1]

[0084] 3.Results As shown in Table 1, for samples S6 and S15, which contained TiO2 in the oxide film and did not contain TiO, delamination between the oxide film and the glass seal portion was observed in a tensile test after applying a voltage of 5V. Reduction expansion of the oxide film due to voltage application was observed, and it is thought that this caused the delamination. For samples S9 and S18, which contained TiO2 in the oxide film but did not contain TiO, delamination between the oxide film and the glass seal portion was observed in a tensile test after applying a voltage of 5V. It is thought that the poor bonding between the metal member and the glass seal portion caused the delamination.

[0085] For other samples containing both TiO2 and TiO as titanium oxides in the oxide film, no cracks or delamination were observed in tensile tests after applying a voltage of 5V. Of these, samples S2-S4, S7, S8, S11-S13, S16, and S17, which had a titanium oxide content of 0.1% to 10% by mass, also showed no cracks or delamination in tensile tests after applying a voltage of 10V.

[0086] B. Variations: The technologies disclosed herein are not limited to the embodiments described above and can be modified in various forms without departing from their essence, for example, the following modifications are possible. (1) In the above embodiment, the glass seal portion 135 was an interposed member between the single-cell separator 120, which is a metal member, and the IC separator 180, which is another member. However, the glass seal portion may also be an interposed member between, for example, the single-cell separator, which is a metal member, and the single cell. (2) In the above embodiment, the metal member was a single-cell separator 120 and the other members were IC separators 180, but for example, the metal member may be an IC separator and the other members may be single-cell separators. Alternatively, the metal member may be an IC separator and the other members may be interconnectors, or the metal member may be interconnectors and the other members may be IC separators. (3) In the above embodiment, the fuel cell stack 10 was configured to include a plurality of flat-plate type single cells 110, but the electrochemical reaction cell stack may also include other types of single cells (for example, cylindrical, flat cylindrical). (4) In the above embodiment, an example was shown in which at least one of components i) and ii) is included in the adjacent region of the oxide film, but at least one of components i) and ii) may be included in a region of the oxide film that is different from the adjacent region. (5) For example, as shown in Figure 7, if the glass seal portion 135 is joined near the corner of the single-cell separator 120B, the adjacent region Ar2nB may be a portion of the oxide film 122B that is bent along the corner. (6) In the above embodiment, the electrochemical reaction cell stack was a cell stack used in a solid oxide fuel cell (SOFC). However, the above configuration is also applicable to cell stacks used in other types of fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and molten carbonate fuel cells (MCFCs), or to electrolytic cell stacks that include electrolytic cell units, which are constituent units of solid oxide electrolytic cells (SOECs), as single cells. [Explanation of symbols]

[0087] 10: Fuel cell stack (electrochemical reaction cell stack) 100: Power generation block 100U: Electrochemical reaction unit 110: Single cell 112: Electrolyte layer 114: Air electrode 116: Fuel electrode 118: Reaction prevention layer 120, 120B: Separator for single cell (metal component) 121: Through hole 122, 122B: Oxide coating 124: Sealing material 130: Air electrode frame 131: Through hole 132: Sealing hole 135: Glass seal part 140: Fuel electrode frame 141: Through hole 144: Fuel electrode current collector 145: Electrode opposing part 146: Interconnector opposing part 147: Connecting part 149: Spacer 180: Separator for IC 181: Through hole 190: Interconnector 191: Flat plate part 192: Air electrode current collector 193: Coating layer 196: Conductive bonding material 210: First end plate 211: Flat section 212: Through hole 213: Outer protrusion 214: Inner protrusion 220: Insulating section 230: End separator 231: Through hole 232: First plate 240: First terminal plate 241: Through hole 250: Second terminal plate 260: Second plate 270: Second end plate 271: Flat section 272: Through hole 273: Outer protrusion 274: Inner protrusion 280: Gas passage member 281: Main body section 282: Flange section 283: Gas through hole 284: Bolt hole 311: Oxidizer gas supply manifold 312: Oxidizer gas discharge manifold 313: Air chamber 321: Fuel gas supply manifold 322: Fuel gas discharge manifold 323: Fuel chamber Ar1: Contact area Ar2: Non-contact area Ar2n, Ar2nB: Proximity area B: Bolt BH: Bolt hole FG: Fuel gas FOG: Fuel off-gas N: Nut OG: Oxidizer gas OOG: Oxidizer off-gas

Claims

1. A single cell comprising a fuel electrode, an electrolyte layer, and an air electrode, A metal component made of a chromium-containing alloy having an oxide film on its surface, A glass seal portion interposed between the metal member and other members, or between the metal member and the single cell, and in contact with the oxide film, Equipped with, An electrochemical reaction cell stack wherein the oxide film comprises at least one of the following components i) and ii). i) a) and b) below a) TiO and Ti 2 O 3 at least one of the b) Unclear 2 ii) c) and d) below c) NbO and Nb 2 O 3 at least one of the d) NbO 2 and Nb 2 O 5 at least one of the

2. The oxide film has a contact region that is in contact with the glass seal portion and a non-contact region that is not in contact with the glass seal portion. At least one of the above components i) and ii) is included in the proximity region of the non-contact region, where the distance measured along the surface of the oxide film from the boundary position with the contact region is 100 μm or less. The electrochemical reaction cell stack according to claim 1.

3. The content of TiO of the components i) and ii) in the proximity region ２ and NbO ２ in terms of conversion is 0.1% by mass or more and 10% by mass or less The electrochemical reaction cell stack according to claim 2.

4. The glass seal portion is SiO 2 -B 2 O 3 - Made of MgO-based glass, The electrochemical reaction cell stack according to claim 1 or claim 2.

5. A single cell comprising a fuel electrode, an electrolyte layer, and an air electrode, A metal component made of a chromium-containing alloy having an oxide film on its surface, A glass seal portion interposed between the metal member and other members, or between the metal member and the single cell, and in contact with the oxide film, Equipped with, An electrochemical reaction cell stack wherein the oxide film comprises the following components e) and f). e) MO and M 2 O 3 at least one of the f) MO 2 and M 2 O 5 at least one of the (However, M represents transition metal elements excluding chromium.)

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